A core drill as well as a drilling tool, a so-called drill bit, are the essential requirements for carrying out a core drilling or hollow core drilling. The core drill includes, in principle, an electric motor as a drive and for generating a torque, as well as an output shaft for transmitting this torque. The drill bit is made up essentially of a cylindrical hollow body (steel casing) having a diamond segmentation at a cutting end and an attachment piece at a fastening end. The drill bit is fastened with the attachment piece to the output shaft of the core drill in such a way that the torque generated in the core drill is transmitted to the drill bit. The torque transmitted to the drill bit sets the core drill in rotation, as a result of which the cutting end with the diamond segmentation is rotated into a material and in this way a hole may be drilled into the material. The material is usually mineral rock or concrete.
The output shaft of core drills usually has a simple thread, with which the output shaft or core drill is connected to the attachment piece of the drill bit. A threaded connection of this type is referred to, for example, as a BS interface. To install or remove the drill bit on or from the output shaft of the core drill, a special tool in the form of a (screw-) wrench is normally required. Correctly tightening the thread as well as loosening of the thread without this special tool and merely by hand is extremely difficult or even impossible. The often times extremely high torque transmitted by the core drill to the drill bit may result in a very strong force-fit in the thread between the output shaft and the drill bit.
A tool holder for a drill bit for fastening to a core drill is described, for example, in European Patent Application EP 1424 152 A1 in the form of a thread according to the prior art. In this case, a chucking end of the drill bit includes an external thread flange and a gear shaft of the core drill and an internal thread flange. The external thread flange and the internal thread flange are axially tightened to one another in order to fasten the drill bit to the gear shaft.
In tool holders according to the prior art presently on the market, undesirable effects may appear in the event of extreme strain. Thus, for example, the screw fitting between the output shaft and the drill bit may become loose as a result of vibrations and shocks during core drilling. Vibrations and shocks during core drilling may, however, also result in an even tighter force-fit in the thread between the output shaft and the drill bit, so that the thread may be loosened again only with very great effort. Contaminants resulting from accumulating drill dust or deformations as a result of an external force effect may cause damage to individual components of the tool holder, which, in turn, may result in a malfunction or in a complete failure of the tool holder.